added mini model; removed stale tests and resources

src/main/java/gov/usgs/earthquake/nshmp/calc/Site.java

src/main/java/gov/usgs/earthquake/nshmp/calc/Sites.java

...java/gov/usgs/earthquake/nshmp/model/SourceConfigOld.java

...est/java/gov/usgs/earthquake/nshmp/model/LoaderTests.java

.../java/gov/usgs/earthquake/nshmp/model/ModelInfoTests.java

...va/gov/usgs/earthquake/nshmp/model/SourceConfigTests.java

.../resources/model/model-minimum/active-crust/gmm-tree.json

src/test/resources/model/model-minimum/calc-config.json

src/test/resources/model/model-minimum/model-info.json

src/test/resources/model/model-minimum/source-config.json

src/test/resources/model/model-no-config/model-info.json

...el/model-no-gmm-tree/active-crust/intentionally-empty.txt

src/test/resources/model/model-no-gmm-tree/model-info.json

...test/resources/model/model-no-gmm-tree/source-config.json

src/test/resources/model/model-no-info-data/model-info.json

...est/resources/model/model-no-info/intentionally-empty.txt

...test/resources/model/model-no-source-dirs/model-info.json

...t/resources/model/model-no-source-dirs/source-config.json

...sources/model/model-no-sources/active-crust/gmm-tree.json

src/test/resources/model/model-no-sources/calc-config.json